A new study led by Weizmann Institute of Science scientists reveals that the intensification of winter storms in the Southern Hemisphere has already reached the level of predictions for the end of the 21st century
However, it seems that the next UN report will also have to take into account the surprising findings of a new study published today in the scientific journal Nature Climate Change. A team of researchers led by Dr Rai Chamka from the Department of Earth and Planetary Sciences at the Weizmann Institute of Science - in collaboration with Dr. Yi Ming from Princeton University and Dr. Yani Yuval from MIT - reveals a significant strengthening of the intensity of winter storms in the Southern Hemisphere. So far, climate models have predicted that human activity, which increases carbon dioxide emissions into the atmosphere, will lead to a significant strengthening of winter storms only later this century. In the new study, the scientists compared the data that emerged from the running of the climate dynamics models and the findings of actual observations and discovered that the strengthening of the storms had already reached a level that was expected to occur at the end of the 21st century.
About 30 large and particularly complex computer networks are at the forefront of climate research. Each of them runs a model that consists of millions of lines of code, and calculates the countless physical, chemical and biological phenomena that create the environmental conditions on Earth over hundreds and thousands of years. The models teach us about the state of the atmosphere, the oceans, the continents or the glaciers, looking back on the environmental history and for the purpose of providing forecasts for the expected climate changes in the decades and hundreds of years to come. These results are analyzed by leading research institutes in the world, including the Weizmann Institute of Science, and based on them the comprehensive reports of the United Nations on climate change are written (IPCC reports) and the global policy is determined to deal with one of the biggest challenges of our generation.
Winter storms are indeed a weather event that lasts only a few days, but cumulatively they create currents of energy (heat and moisture) in the atmosphere - thus affecting the various climate zones around the globe. For example, the storms are responsible for most of the heat "transportation" from the tropical region to the pole, so without their influence, the average temperature at the poles would be about 30 degrees lower. The long-term impact of winter storms is revealed when averages are calculated from data accumulated over very long periods of time. This, in a similar way to climate research, which distills phenomena that can be measured and calculated and that occur over large spans of time and space. Therefore, the surprising strengthening of storms in recent years has significant climatic consequences.
The researchers chose to focus on the Southern Hemisphere because that is where the intensity of the storms is stronger. The study did not examine the situation in the Northern Hemisphere, but apparently, the strengthening of storms in this region is less compared to the Southern Hemisphere and will be felt in the coming decades.
Changes in the structure of the jet streams in the atmosphere
Chamka, who studies the physics governing climate change in his lab at the institute, and his partners in this research, wanted to make sure that the strengthening of the winter storms is due to external constraints on the system (such as human activity) - and that it is not a question of changes that occur naturally in the climate system. To this end, they analyzed simulations of climate models that examined the range of possible changes in the intensity of the storms as a result of internal factors only, and without the influence of external constraints such as human activity. They discovered that already two decades ago, the strengthening of the storms exceeded the maximum range of the "noise" in the system that may be caused by internal sources. In addition, the researchers discovered the fiscal process that causes the storms to intensify: an analysis of the growth rate of the storms revealed that changes in the structure of the jet streams in the atmosphere in recent decades caused the storms to intensify, and it seems that the climate models are unable to reproduce these changes with the correct intensity.
The research has two immediate and significant consequences: one, it shows that not only are the climate forecasts for the rest of the current century likely to be more severe than we estimated, but it is also possible that human activity has a greater impact on the climate in the Southern Hemisphere than was known until now. Therefore, the urgency to act more quickly and decisively to mitigate climate damage in this region is increasing. Second, it is necessary to correct the climate forecasting models by which the policies of governments in dealing with climate change are determined, in order to provide a more accurate forecast of the changes in the intensity of storms in the coming decades.
Following the findings, the question arises, do the Earth's climate models miss other important phenomena? Chamka reassures: "The models do a good job in almost all indicators, such as, for example, in identifying temperature changes, the amount of precipitation or ice and summer storms. We discovered one index where there is an error in the sensitivity of the models, and it needs to be corrected."
The results of the study are expected to help climate researchers in the world correct the deviation in the models, and produce a more accurate forecast for the future. Furthermore, they may help climate scientists assess how much worse our situation has become following the discovery that winter storms have gotten so much stronger in recent decades - a trend that may worsen as long as the world does not find solutions to the climate crisis.
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